1. Field of the Invention
The present invention relates to a semiconductor device including a ferroelectric capacitor structure formed by sandwiching a ferroelectric film between a lower electrode and an upper electrode.
2. Description of the Related Art
In recent years, the development of a ferroelectric memory (FeRAM) which holds information in a ferroelectric capacitor structure using polarization inversion of a ferroelectric has been advanced. The ferroelectric memory is a nonvolatile memory in which held information is not erased even if the power is turned off, and attracts special attention because it is expected to be able to realize high-density integration, high-speed driving, high durability, and low power consumption.
Mainly used as a material for a ferroelectric film constituting the ferroelectric capacitor structure is a ferroelectric oxide having a perovskite crystal structure such as a PZT(Pb(Zr, Ti)O3)) film, a SBT(SrBi2Ta2O9) film, or the like with a large remanent polarization amount, for example, from about 10 (μC/cm2) to about 30 (μC/cm2).
It is known that in the ferroelectric capacitor structure, the characteristic of a capacitor film made of the ferroelectric deteriorates due to water which has penetrated from the outside through an interlayer insulating film such as a silicon oxide film having a high affinity to water. Namely, first, the water which has penetrated from the outside is decomposed into hydrogen and oxygen during a high-temperature process when the interlayer insulating film and a metal wiring are formed. When penetrating into the capacitor film, this hydrogen reacts with oxygen in the capacitor film to thereby form oxygen deficiency in the capacitor film, which results in a reduction in crystallinity. The same phenomenon occurs also by prolonged use of the ferroelectric capacitor. As a result, deterioration in the performance of the ferroelectric capacitor structure such as a reduction in the remanent polarization amount and dielectric constant of the capacitor film occurs. Further, the performance of not only the ferroelectric capacitor structure but also a transistor or the like sometimes deteriorates due to such penetration of hydrogen.
As a way of dealing with this problem peculiar to the FeRAM, it is proposed that a hydrogen diffusion preventing film made of alumina or the like is formed so as to cover the ferroelectric capacitor structure. This hydrogen diffusion preventing film makes it possible to prevent hydrogen from penetrating into the capacitor film and hold the high capacitor characteristic of the FeRAM.    (Patent Document 1)    Japanese Patent Application Laid-open No. 2003-174095    (Patent Document 2)    Japanese Patent Application Laid-open No. 2002-26287    (Patent Document 3)    Japanese Patent Application Laid-open No. 2002-151659
Incidentally, when an opening (via hole) for wiring connection is formed for the ferroelectric capacitor in a state where the interlayer insulating film is formed so as to cover the ferroelectric capacitor of the FeRAM with the hydrogen diffusion preventing film therebetween, the interlayer insulating film and the hydrogen diffusion preventing film are dry etched so that the position of the surface of the ferroelectric capacitor is exposed (See Patent Documents 1 to 3). However, in this case, plasma at the time of dry etching sometimes causes damage to the ferroelectric capacitor. There is a problem that to recover this damage, it is indispensable, for example, to perform annealing in an O2 atmosphere, so that an increase in the number of steps is inevitable.
Further, due to dry etching, unwanted residuals such as an etching residue and a scum occur in the opening and on the interlayer insulating film, and the residuals contribute to a reduction in the reliability of the ferroelectric capacitor.